Legacy System Migration to Advanced Digital System
Published on : Friday 06-08-2021
Jasbir Singh elaborates on the process of migration from legacy systems to advanced digital configuration.
Modifications in the process line or control system in manufacturing setup always require greater planning, confidence of its future performance, a length of training to the operator, supporting and maintenance staff and committed management support. It is important for a gradual digitalisation in the manufacturing sector for process automation. The common philosophy used while plant expansion is integration of current assets (having no bottleneck) with a new system for seamless transaction. Existing units are sometimes added with modern production units/systems for capacity expansion or improving product features.
Modernisation in processes and controls
Legacy is a word often heard during a discussion when users want to improve productivity. Legacy systems mainly refer to both manual/semi-automated machines and the control system used to drive them. Industry is compelled to use the current so-called legacy system till it provides the user the needs with required productivity, consistent performance, no abrupt failures and quick recovery in case of failure, which can affect the customers or end users. The decision to keep a legacy system is predominantly influenced by economic reasons; these include fund availability and longer return on investment and longer shutdown to replace, as the production unit has to be kept running. The driving forces to change the current system on the other hand are its functionality, ease of maintenance, low recovery time in case of failure, speed and high productivity.
Normally it is advised to transfer the monitoring of the data to a new and advanced digital platform. For any such change the data exchange is required from the present control system to a new database of advanced control systems. Data visibility enables companies to be consistently productive and deliver under safe operation. Intelligent automation technology is used to collect the field data from existing legacy systems along with new additional units using the latest technology. The system is required to be connected with advanced master controllers installed in the main control room for remote access, without compromising operational safety. Operation of large plant functions safely only with open, secure and flexible communication solutions. It utilises available process data for efficient system operation and enables engineers to analyse the current performance and anticipated future outputs to reap the best out of the capacity expansion.
Suggested migration model
Historical data from legacy systems and its integrated use for the entire system is a challenging task. Conversion of historical data in a new user’s format and establishing its connectivity with a new controller for real time control shall always be beneficial to operators for quality improvement.
In addition, there are challenges that often surface while integrating with newer technology, advanced systems, design applications, backward integration and software development of controllers. The life cycle of control system technology is becoming shorter as the days pass due to the evolution of new technology/speed of execution and ease of operation. The expectations of customers are constantly evolving for the advanced control, hyper-connected bus for data exchange flexibility, ease of troubleshooting in case of failure and lower interruption time in production line. Digital control systems have always been under unrelenting pressure to support advance/leading-edge capabilities of cybersecurity and integration with third-party systems. The vendors are mostly the same, but the technology, applications, hardware and principles of the past do not become valid in current time. Systems, which were capable of operating the units a few years ago, are now rapidly becoming obsolete. IoT is becoming part of real life where sensors are digitised, connected with internet/wifi to provide real time process information and its health condition simultaneously.
Improvement efforts towards integrated digitalisation must focus to create value for the enterprise in the current competitive edge environment. Before taking decisions for improvements or modernisation of manufacturing units it is essential to know the right digital platform/control system having flexibility in peer to peer connectivity with new digital systems. The outdated Distributed Control System/Programmable Logic Controller used in manufacturing units became important to update or migrate into advanced control systems to stay competitive. It will improve flexibility for product expansion, capacity expansion and easy product change in the same line with low idle time/outage of machine during changeover. The legacy systems might have served them well in the past, but as digital technology evolves, upgrading is inevitable to meet ever-changing consumer demands.
Dawn of digital era
The process control in the manufacturing industry (fertilizer, refineries, pharmaceutical, and chemical plants) were migrated from pneumatic control and then to relay logic control to distributed control systems (DCSs). The cutting-edge systems of that time had brought value-added technologies where graphical operator displays/control and easy data analysis software relieved operators from cumbersome processes to pinpoint failures, diagnostics and quicker alarm response. The control strategies were possible to be tested before implementation. Offline system engineering of control systems to develop application software became easy and less time consuming. New and complex control strategies are possible to add at any stage of engineering.
The following ISA standards play active roles for system standardisation
1. ISA-95 Enterprise-Control System Integration
2. ISA-18.2 Alarm Management
3. ISA-88 Batch
4. ISA-99 Cyber-Security
5. ISA-100 Wireless
6. ISA-101 HMI
7. ISA-103 Field Device Tools
8. ISA-106 Procedural Automation
9. ISA-108 Intelligent Device Management.
Evolution/transformation in digital technology
Knowing all of the above is not the only thing that remains in the present day context. In the prevailing digital era the evolution of complex hardware and software is much faster compared to even change in overall control strategy in progression of every generation. DCS/PLC platform provides major support to develop control strategies for complex operations in manufacturing. The system vendors keep on developing the future need of business. The drivers are mainly faster/easy logic and control loop generation, tool based application software creation and offline testing for safe and high speed operation in plants. The systems are functionally divided in three systems, such as process control system (PCS), safety integrity system (SIS) and fire and gas (F&G) system, connected with the same human machine interface (HMI). However each system has different types of hardware and software to function and configured with dedicated engineering terminals. Development of computer and IT systems are directly linked to advance DCS development and software generation platforms such as UNIX to window based systems.
Control system migrations and production system improvements are mainly aimed towards satisfying business drivers. Hardware obsolescence due to loss of its functional values and limited software generation flexibility are the main drivers for migration. If the component fails, the risk associated with unplanned downtime could be enormous in terms of financial cost and safety. It becomes largely difficult to identify the stoppage whether it is due to failure of component or process disturbance/failure. The inherent safety issue with older DCS/PLC served past its life has the chances of continuous process interruptions due to aging of components makes the business non profitable. This leads to sporadic or random failures, which by its nature is difficult to identify. Such intermittent failures can frequently stop the running units, which cause various losses and these unplanned outages sometimes become extremely costly.
DCS migration minimises the risks to maintain older systems and presents the opportunities to take advantage of advanced technologies available. It provides more flexible window based user friendly operator interfaces, more open platforms for larger connectivity with other sub systems, powerful cybersecurity, and superior self-diagnostic capabilities, which can enhance production throughput and reduction in maintenance costs. To keep continuing the operation and production of plant phased migration are the best options. System vendors provide optimal migration blueprint in association with plant operators and engineers to address every need while migration to a new system. Phased migrations typically take place over a long duration of time but it ensures that the system is reliably operable even during the process of migration and operators become well familiar with the new system. The important consideration in every migration process is the flexibility of connections with vendor neutral higher-level systems and subsystems to overcome the limitation of proprietary interfaces.
Advanced DCS systems generally provide a virtual test function as part of flawless software development. The user can virtually operate the system via an HMI, which can test the complete control loops and logic functions defined to operate the unit before the new system actually connects to the plant network to operate. The quality of applications/safety logic during abnormal situations can be further improved if needed using the virtual test function.
Legacy system conversion tool for engineering
The software engineering information like tag numbers, units, ranges, comments, control schemes, alarm settings, tuning parameters, etc., from legacy systems can be directly fed to the new version of system using a template based conversion tool to save time and improve functional reliability. Automatic mapping features are available to map between legacy software and new DCS system control engineering.
Steps to migration (minimisation of cutover time and risk):
1. Use existing cable terminal marshalling panels connected to field devices at field and DCS side.
2. Avoid cabinets rewiring in existing marshalling panels.
3. Use a new marshalling panel terminal for additional loops, if any.
4. Select the quick coupler for signals exchange from the DCS marshalling terminal panel to the system panel.
5. Replace all system panels, power distribution system panel and HMI as a whole.
6. Install all the new panels at different locations nearby.
7. Connect the new HMI with the new DCS system.
8. Load pre offline tested application software at DCS system and HMI (graphic monitors).
9. Test the earthing connection (system, panel and power) of all panels.
10. Final migration by removal of old DCS terminal couplers with respective quick couplers of the new system.
11. Switch-on power and test all field loops individually.
12. Start the process plant.
The plant PLC/DCS unit controllers are generally operated by local controllers during commissioning/shutdown period but simultaneously supervised remotely by engineers from the main control room. After gaining enough confidence the current controller of the legacy system is allowed to be controlled remotely by an advanced digital supervisory main controller at CCR (central control room).
Jasbir Singh is an Automation Expert having long experience in Factory Automation, Line Automation, Implementation Strategist, Business Coach, Regular writer on automation, Artificial Intelligence, Robots/Cobots, Digital Technology, Network Communication, Industrial Internet of Things (IIoT), Wireless Communication, Block Chain and use of advance digital technologies. He has established a long association with Business Houses/large production houses to improve factory automation in their production lines as well as productivity improvement in factories in India and overseas; and in advising and designing the units to transform into digital platforms by use of Artificial Intelligence. Email: [email protected]
